#include <stdio.h>
#include <math.h>

int main(){
    int N;
    double i;
    double sum = 0;
    double n;
    float a = 1;
    scanf("%d",&N);
    for(i=1;i<=N;i=i+1){
        n = i / a * pow(-1,i+1);
        sum = sum + n;
        a = a + 2;
    }
    printf("%.3f\n",sum);

    return 0;
}